1. Field of the Invention
The present invention relates to an automatic liquid-supply stopper plug, and more particularly to a plug for stopping liquid supply automatically when the level of the liquid arrives at a preset level.
2. Description of the Prior Art
The automatic liquid-supply stopper plug of the conventional type has a valve which is closed instantaneously to stop liquid supply when the liquid level arrives at a preset level. As a result, the pressure in the piping at the liquid feed side is abruptly changed due to water-hammering, leading to generation of striking harsh sound or leading to breakdown of liquid feed piping or damage of the automatic water-supply stopper plug per se at the worst.
In order to abate the water-hammering action, it has been proposed to provide an air chamber at the liquid feed side of the automatic water-supply stopper plug to absorb the hammering action. However, provision of such an air chamber is accompanied with disadvantageous increase in production cost. Particularly, when the plug is incorporated in a large-scale liquid supply system through which a large amount of liquid is fed at a high rate, an air chamber having an extremely large capacity must be provided, which results in unacceptable increase in cost.